Torsional vibration balancers with a viscous damping medium and external seismic mass are known, e.g., from German Pat. No 1,297,410. In these devices, the inner primary element is surrounded by the annular seismic mass, the primary element being connected to the shaft to be damped, e.g., the crankshaft of an internal combustion engine. For devices of such construction, two annular seals for retaining the damping medium in the working chambers must be provided between the primary element and the external seismic mass. The seals employed for this purpose in prior art dampers, due to the very frequent small sliding movements, are subject to unavoidable wear, so that they do not reliably seal off the creeping damping medium, silicon oil.
In the device according to German Pat. No. 1,074,333, prevulcanized or glued on seal rings are used, while German Pat. No. 1,132,387 discloses the use of pressed in elastomer bands for sealing purposes. Such seals have a negative effect on the damper because of their significant restoring moments and the material damping, so that the performance limits of the device are often determined to a greater extent by the resistance to sliding of the seals than by the capacitance of the damping medium.
Moreover, such seals, especially in the case of larger damper diameters, are very difficult to produce and to join.
A further disadvantage of torsional vibration balancers with external seismic mass arises from the fact that the required surface of the working aperture in which the damping medium is alternatingly sheared can be prepared only with great effort. For example, in the device disclosed in German Published Application No. 23 61 956, several discs are arranged in the median plane of the damper for the purpose of enlarging its fluid-moistened surface. Since the primary side mass moment of intertia is to remain small, such discs must be stamped from thin, large area sheets. The required stamping apparatus for large dampers is uneconomical, and in their installed condition the metal rounds tend to distort in such a manner that a constant aperture width cannot be assured.